Neuroscience research with animal models implicates neuroadaptation in the stress response as a critical mechanism in the etiology of addiction across multiple classes of drugs including nicotine. Repeated homeostatic adjustments in the brain's stress systems due to chronic drug administration eventually lead to persistent compensatory adaptations in the structures involved in emotional response and its regulation. Among smokers, these stress neuroadaptations result in deregulated negative affect when nicotine-deprived and provide the strong motivational press for further smoking that manifests as urge and increased risk for smoking cessation failure. Animal models have provided substantial evidence to support this stress neuroadaptation thesis in addiction However, programmatic laboratory research that examines the stress response in nicotine deprived and non- deprived smokers (relative to non-smokers) is necessary to confirm that our understanding of stress neuroadaptations from animal models translate to addiction etiology in smokers. Negative affect is the core motivational element of the human drug withdrawal syndrome across additive drugs including nicotine. Unfortunately, much of what we know about these motivationally critical affective processes in humans is based on a narrow range of measures collected in isolation. The examination of the characteristics and neurobiological substrates of negative affect has not kept pace with the rapid conceptual, methodological, and measurement advances in the affective sciences over the past decade. Moreover, complementary methods (e.g., laboratory task manipulations, clinical treatment interventions) and measurement approaches (e.g., psychophysiology, ecological momentary assessment) are rarely combined. The research in this application capitalizes on recent research with both animals and humans that has synthesized precise laboratory manipulations of stress with sensitive psycho physiological measurement of startle reflex potentiating to parse the affective response to stress into its constituent components. In particular, startle potentiating during uncertain (vs. certain) threats holds promise as a biomarker of stress neuroadaptation following chronic nicotine or other drug use. We propose to measure stress neuroadaptation in the laboratory via startle potentiating during uncertain threat in two validated cued threat tasks among nicotine deprived and non-deprived smokers and non-smokers. Smokers will be subsequently assigned to combo NRT or placebo during smoking cessation treatment and will report on episodic stressors, negative effect, smoking urge, and smoking via ecological momentary assessment procedures. Treatment outcome will be assessed at 2 weeks post-quit. The broad goals of this research are to identify etiologically relevant psycho physiological biomarkers of stress neuroadaptation that results from chronic smoking. We evaluate the impact of this stress neuroadaptation on smokers' real-world affect, urge and smoking during smoking cessation treatment. We also evaluate if NRT can attenuate the influence of this stress neuroadaptation on smoking cessation outcomes via its effects on withdrawal.